According to St. Francis Dam historian J. David Rogers, the floodwaters have removed the earthen material supporting the Southern Pacific Railroad tracks
at Castaic Junction (Castaic switch).

Click image to enlarge.

Click image to enlarge.

As he shows in the two images above, local historian Jason Brice places the 1928 photographer southwest of the junction, looking northeast.

Click image to enlarge.

J. David Rogers writes (2014): Here is a clip from my flood inundation map of (the Castaic Junction) area.
The flood waters diverted around the north side of the promontory would have swept in from the east, nearly perpendicular to that tracks in vicinity of Oberg Siding,
and the erosion would have been severe along the oversteepened banks along the eastern side of the Santa Clara River Channel, which is noticeably incised.
That explains how the tracks shifted 200 feet to the west.